A standard freight pallet is a rigid load-supporting structure normally having a planar top formed by a single panel or a plurality of coplanar planks and feet formed as a plurality of parallel cleats secured underneath the top. Such a pallet is described in French Pat. No. 2,301,441.
In my copending patent application Ser. No. 219,859 filed Dec. 23, 1980 I disclose a method of making a pallet wherein a mass of coarse and fine particles and a binder is filled into an upwardly open elongated mold of generally regular cross section in such a manner that the fine particles are concentrated in the lower portion of the mass and the coarse particles are concentrated in the upper portion of the mass. The mass of particles is then compressed downward in the mold to a relatively great extent at several longitudinally spaced locations and to a lesser extent therebetween to form upwardly projecting bumps between the locations. The thus compressed mass is then cured into a stiffening rib or cleat. At least one board is secured to a plurality of such ribs or cleats arranged parallel to one another.
It is also known, as for example from German patent document No. 2,508,493 and from U.S. Pat. Nos. 3,104,085, 3,342,146, and 4,303,019, to make the entire pallet as a single integral molded element formed of cellulosic, that is plant-origin, particles and an appropriate thermosetting binder. Such pallets are normally relatively weak, being particular susceptible to damage from bending. It has been suggested in German patent document No. 3,035,701 to compress the structural members constituting the cleats more between the feet than at them to increase their strength and resistance to breaking in this region. Although an increase in strength is obtained in this manner the resultant pallet is still considerably weaker than a standard solid-oak pallet.
I describe in above-cited parent application Ser. No. 461,604 a method of making an elongated structural member from elongated cellulosic particles and a binder wherein a mass of the particles and binder is randomly filled, that is with the particles not extending parallel to one another although a stratified filling according to my earlier invention may be used, into a horizontally elongated compartment defined between a pair of elongated and horizontally confronting side walls having central portions, an elongated top wall, and an elongated bottom wall confronting the top wall and extending generally parallel to the top and side walls. The top and bottom walls are then displaced vertically toward each other into predetermined intermediate positions without substantial movement of the side walls so as to vertically compress the mass in the compartment. Thus the particles engaging the top and bottom walls are aligned generally therewith. At least the central portions of the side walls are then displaced horizontally toward each other between the top and bottom walls without substantial movement of the top and bottom walls from their intermediate positions so as to horizontally compress the vertically compressed mass in the compartment, Finally the top and bottom walls are displaced vertically toward each other into terminal positions to further vertically compress the mass in the compartment without substantial movement of the side walls. The mass is then cured and hardened between the walls without substantial movement of same.
Such pallets are inexpensive to manufacture and are relatively durable. Nonetheless they are often inadequately strong, in particular when bent or unevenly loaded, and are subject to rapid disintegration in particular when they must stand on a wet surface or are slid about a great deal on a rough surface.